Hidden ADU Costs Nobody Puts in the Brochure

Per-square-foot math captures the building. It misses the project. These are the costs that show up in real budgets and rarely in brochures.

Demolition and hauling ($2K–$10K). Old sheds, concrete patios, that dead spa — whatever occupies the ADU's future spot must be demolished and hauled. Dumping fees are real and rising.

Dirt export ($2K–$8K+). Foundations produce excavated soil, and soil is astonishingly expensive to make disappear. Sloped lots exporting more pay more.

Landscape and hardscape repair ($3K–$15K). Trenches cross your yard; equipment crosses your lawn; the fence panel comes off for access. The construction is scoped; putting your yard back usually isn't. Ask what the bid excludes.

Temporary power, water, and facilities ($1K–$3K). Construction consumes utilities and requires a porta-potty for months. Small, but it's on somebody's tab — know whose.

Appliances ($3K–$8K). Many construction contracts exclude appliances entirely. The unit needs a fridge, range, and (please) a washer/dryer before anyone can live there.

Window coverings, screens, closet interiors ($1K–$4K). The "move-in ready" gap. Tenants notice bare windows immediately.

Insurance and carrying costs. Course-of-construction insurance, an updated homeowner's policy, and — if you're financing — months of loan interest before rent begins. Financing an ADU with a construction loan? Interest during the build is a real five-figure line on larger projects.

Utility deposits and meter fees ($500–$5K+). Separate meters carry utility charges of their own (Module 7).

Vacancy and lease-up. The unit finishes; the tenant arrives 4–8 weeks later. Budget the gap.

The fix is boring and works: demand itemized bids listing exclusions explicitly, and add the excluded reality back into your own master budget. The scary number up front beats the surprising number in month eight.